(Not Applicable)
Reference to an appendixxe2x80x9d
(Not Applicable)
1. Field Of The Invention
This invention relates generally to cellulose insulation of the type utilizing a shredded newspaper base which is treated with a fire retardant chemical composition and used for the thermal insulation of homes and other building structures. More particularly, the invention relates to the addition of a specific range of antistat and electrostatically positively charged fibrous materials to the newspaper base which will lower density and reduce settling of the insulation.
2. Description Of The Related Art
The manufacture of cellulosic insulation, in accordance with the present state of the art, begins with a grinding operation in which newspapers are shredded to a level of approximately 1xe2x80x3xc3x971xe2x80x3 pieces and individual fibers. These fibers and paper pieces, carried in air stream, are then ground in a second operation in which finely ground fire retardant chemical is added to the paper and paper pieces.
The key to the understanding of the underlying basis of cellulose insulation is to recognize that cellulose insulation is made up of newspaper pieces and fibers which are affected by static electricity. Like elements will repel; unlike elements will attract. A method of determining the electrostatic charge of a material piece or fiber is to rub the flat side of a nylon toothbrush about 50 times on a piece of wool. Then attempt to attract the material in question with the flat side of the toothbrush. If the material is positively charged, it will attach to the flat part of the toothbrush. If the material is negatively charged, it will not be attracted to the flat base of the toothbrush, but may attach to the edges of the toothbrush. Based on the above system, the face of a newsprint paper piece is positively charged and the edge fibers are negatively charged. The newspaper separate fibers are also negatively charged.
U.S. Pat. No. 4,468,336 refers to an insulation xe2x80x9cwherein the loose fill cellulose insulation has a settled density on the order of about 2.5 pounds per cubic foot before mixing with staple fibers, and the mixture of cellulosic insulation with from 2% to 25% by weight staple fibers has a settled density in the order from 2.1 pounds per cubic foot to about 1.1 pounds per cubic footxe2x80x9d. Staple fibers were defined as acrylic, polypropylene, acetate etc. These fibers are electrostatically positively charged.
Because the paper pieces were positively charged, the surface of the paper piece attracted negatively charged paper fibers, essentially parallel to the face of the paper piece. This attraction caused the paper piece to become neutrally charged and therefore, no longer statically attractive. Therefore, the positively charged staple fibers attracted most of the remainder of negatively charged paper fibers, forming a phase separate from the paper pieces. This separate phase is not settling stable because this structure is not supported by the paper pieces and vertically oriented fibers attached to the edges of the paper pieces and will condense. It took a large amount of the staple fibers to lower the cellulose density by producing a separate, lower density, paper fiber to positively charged fiber structure.
In an attempt to improve settling and density of cellulose insulation, I determined that there was an advantage to produce a specific type of fiber to paper piece structure. In this structure, use of the inorganic, non-hygroscopic powder and antistat mixture as described in U.S. Pat. Nos. 5,399,375 and 5,455,065 reduces the static charge on the paper pieces and fibers to a level where fire retardant chemical will adhere to both the paper pieces and fibers. The preferred structure is where the fibers are attached to the paper piece at an angle to the face of the paper piece, not parallel to the face of the paper piece. In this preferred structure, there are very little separate fiber to fiber groupings.
Examples of inorganic, non-hygroscopic powders useful in this invention are limestone, zinc oxide and silica. The non-hygroscopic nature of the powder will allow the antistat to be fed accurately and spread uniformly, even if some moisture is present.
Electrostatically, positively charged fibers, such or wood or fiberglass added either before or after the addition of the antistat to the partially ground paper, are attracted to the negative edges of the electrostatically charged paper piece. The attached positively charged fibers then attract the negatively charged paper fibers, producing a reinforced structure which reduces density and settling.
Improvements in density and settling result from the fact that the negative fibers are deposited at an angle to the face of the paper piece. Density and settling will depend on the distance between paper pieces, affected by the level of static electricity in the system. The degree of separation of the paper pieces is dependent upon the amount of antistat used; the more antistat, the less the separation and the higher the density. Water addition also reduces static electricity, lowering settling, but the static electricity level is increased when the water dries. The amount of electrostatically positively charged fibers added will vary with the type of fiber used. The key is that the amount of separate, positively charged fibers relative to negatively charged fiber groupings is held to a minimum.
Additional reduction in settling occurs by increasing the amount of antistat beyond that amount necessary to produce lower density. Ultimate settling stability is achieved by reducing the static charges in the cellulose to the point where the cellulose charges are almost neutral. In achieving this reduction in settling, density is increased slightly because the electrostatic charges keeping the fibers and paper pieces apart are reduced. Lowering in settling can be accomplished by the addition of water to the cellulose prior to application, but the level of settling increases once the water evaporates.